The invention relates to a method and to a device for determining torque setpoint values for a motor vehicle having at least two drive assemblies.
Future generations of vehicles will be equipped not only with a conventional internal combustion engine but increasingly also with at least one additional drive assembly, such as a crankshaft starter generator, also referred to below as an integrated starter generator (ISG). A method for controlling a power engine, which includes an internal combustion engine and a crankshaft starter generator, is known from International Publication WO 99/62735. A setpoint value of a torque is determined as a function of the position of the accelerator pedal, the rotational speed and a torque loss. In this torque loss, losses are taken into account as a function of further operating variables such as the air mass flow rate, the coolant temperature, the oil temperature, the current through the crankshaft starter generator and the temperature of the crankshaft starter generator. The air mass flow rate is set based upon a setpoint torque and is also based upon a setpoint torque that is derived from action values of the torque that are needed in functional units for controlling the internal combustion engine such as a traction controller, a rotational speed limiter, a speed limiter or a catalytic converter heating function unit. In addition, a setpoint value of the torque which is to be set within a predefined time period is determined as a function of the setpoint torque and the torque requirements of the other functions. The crankshaft starter generator and the ignition are then actuated as a function of this torque setpoint value which is to be set quickly.
In this method, the additional drive assembly in the form of the crankshaft starter generator is used to implement the torque requested by the driver by activating the accelerator pedal, but during the conversion of the accelerator pedal position into a setpoint torque, only the loss torque of the crankshaft starter generator is taken into account. The possibility of generating an additional torque using the crankshaft starter generator is not taken into account.
It is accordingly an object of the invention to provide a method and a device for determining torque setpoint values for motor vehicles having at least two drive assemblies, which overcomes the above-mentioned disadvantageous of the prior art apparatus and methods of this general type. In particular, it is an object of the invention to provide a method and a device for determining torque setpoint values for motor vehicles having at least two drive assemblies by means of which the characteristic strengths and weaknesses of the individual drive assemblies are taken into account directly during the conversion of a variable which characterizes the driver""s requirement into torque setpoint values.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for determining torque setpoint values for a motor vehicle having at least two drive assemblies. The method includes steps of: providing a motor vehicle having at least two drive assemblies; providing the motor vehicle with a device for sensing a variable that characterizes a driver""s requirement; providing the motor vehicle with a device for sensing operating variables of the motor vehicle; providing a separate evaluation branch for each one of the at least two drive assemblies; determining a respective torque setpoint value in each one of the at least two separate evaluation branches; and determining each respective torque setpoint value as a function of the variable that characterizes the driver""s requirement and as a function of the operating variables of the motor vehicle.
In accordance with an added mode of the invention, the method includes steps of: providing at least one of the at least two drive assemblies as an electric motor; deriving a torque factor for the electric motor from the variable that characterizes the driver""s requirement and as a function of a driver type and/or a charge state of a vehicle battery; and determining an electric motor torque setpoint value from the torque factor for the electric motor and from a rotational speed, the electric motor torque setpoint value defining the torque setpoint value in one of the at least two separate evaluation branches.
In accordance with an additional mode of the invention, the torque factor deriving step is performed by deriving the torque factor for the electric motor in dependence on a gradient of the variable that characterizes the driver""s requirement.
In accordance with another mode of the invention, the torque factor deriving step is performed by deriving the torque factor for the electric motor in dependence on an integral over the variable that characterizes the driver""s requirement.
With the foregoing and other objects in view there is also provided, in accordance with the invention, a device for determining torque setpoint values for a motor vehicle having at least two drive assemblies. The device includes means for determining a torque setpoint value, for each one of at least two drive assemblies, as a function of a variable that characterizes a driver""s requirement and as a function of operating variables of a motor vehicle. The means may be a determination device, for example, a processor.
In accordance with an added feature of the invention, the means is configured to determine the torque setpoint values for individual ones of the drive assemblies in evaluation branches that are separate from one another.
In other words, in motor vehicles having at least two drive assemblies, torque setpoint values are determined for each of the drive assemblies in separate evaluation branches as a function of a variable which characterizes the driver""s requirement and as a function of operating variables of the motor vehicle. Here, the specific strengths and weaknesses of the respective drive assembly are taken into account directly in the respective evaluation branch so that the overall torque setpoint value which results from the sum of the individual torque setpoint values always represents the maximum possible torque under the operating conditions of the motor vehicle applying at a given moment.
In one preferred embodiment, at least one of the drive assemblies is embodied as an electric motor. The torque setpoint value for the electric motor is determined from a torque factor for the electric motor and from the rotational speed. The torque factor for the electric motor is derived from the variable which characterizes the driver""s requirement, as a function of the driver type and/or the charge state of a vehicle battery. The term electric motor is to be understood here and below in a general sense and also includes crankshaft starter generators which are preferably embodied as asynchronous machines, but which also may be embodied as synchronous machines or as d.c. motors.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and device for determining torque setpoint values for drive assemblies of motor vehicles having at least two drive assemblies, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.